287 research outputs found
Impact of VLC on Light Emission Quality of White LEDs
No full textData set for the published paper:
W. O. Popoola, "Impact of VLC on Light Emission Quality of White LEDs," in Journal of Lightwave Technology, vol. 34, no. 10, pp. 2526-2532, May15, 15 2016. doi: 10.1109/JLT.2016.254211
Data set for: 'Impact of VLC on Light Emission Quality of White LEDs', in Journal of Lightwave Technology, vol. 34, no. 10, pp. 2526-2532, May15, 15 2016
No full textData set for the published paper: W. O. Popoola, "Impact of VLC on Light Emission Quality of White LEDs," in Journal of Lightwave Technology, vol. 34, no. 10, pp. 2526-2532, May15, 15 2016. doi: 10.1109/JLT.2016.254211
Enhanced carrierless amplitude and phase modulation for optical communication systems
No full textThis thesis develops and investigates enhanced techniques for carrierless amplitude and phase
modulation (CAP) in optical communication systems. The CAP scheme is studied as the
physical layer modulation technique due to its implementation simplicity and versatility, that
enables its implementation as a single carrier (CAP) or multi-carrier technique (m-CAP).
The effect of timing jitter on the error performance of CAP is first investigated. The
investigation indicates that synchronization is a critical requirement for CAP receiver and as
a result, a novel low-complexity synchronization algorithm is developed with experimental
demonstration for CAP-based visible light communication (VLC) systems. To further reduce
the overall link complexity, a fractionally-spaced equalizer (FSE) is considered to mitigate the
effects of inter-symbol interference (ISI) and timing jitter. The FSE implementation, which
eliminates the need for a separate synchronization block, is shown through simulation and
VLC experimental demonstration to outperform symbol-spaced equalizers (SSE) that are
reported in literature for CAP-based VLC systems.
Furthermore, in this thesis, spectrally-efficient index modulation techniques are developed for
CAP. The proposed techniques can be divided into two broad groups, namely spatial index CAP
(S-CAP) and subband index CAP (SI-CAP). The proposed spatial index techniques leverage
the fact that in VLC, multiple optical sources are often required. The spatial CAP (S-CAP)
transmits CAP signal through one of Nt available LEDs. It is developed to reduce equalization
requirement and improve the spectral efficiency of the conventional CAP. In addition to the bits
transmitted through the CAP symbol, the S-CAP encodes additional bits on the indexing/spatial
location of the LEDs. The generalised S-CAP (GS-CAP) is further developed to relax the
S-CAP limitation of using a single LED per symbol duration. In addition to the S-CAP scheme,
multiple-input multiple-output (MIMO) techniques of repetitive-coded CAP (RC-CAP) and
spatial multiplexing CAP (SMux-CAP) are investigated for CAP. Low-complexity detectors
are also developed for the MIMO schemes. A key challenge of the MIMO schemes is that they
suffer power penalty when channel gains are similar, which occur when the optical sources are
closely located. The use of multiple receivers and power factor imbalance (PFI) techniques
are proposed to mitigate this power penalty. The techniques result in significant improvement
in the power efficiency of the MIMO schemes and ensure that the spectral efficiency gain is
obtained with little power penalty.
Finally, subband index CAP (SI-CAP) is developed to improve the spectral efficiency of
m-CAP and reduce its peak-to-average power ratio (PAPR). The SI-CAP encodes additional
information bits on the selection of ‘active’ subbands of m-CAP and only modulate data
symbols on these ‘active’ subbands. The error performance of the proposed SI-CAP is
evaluated analytically and verified with computer-based simulations. The SI-CAP technique is
also experimented for both VLC and step-index plastic optical fibre (SI-POF) communication
links. The experimental results show that for a fixed power efficiency, SI-CAP achieves higher
data rate compared tom-CAP. For example, at a representative bit error rate (BER) of 10-5, the
SI-CAP achieves a data rate and power efficiency gain of 26:5 Mb/s and 2:5 dB, respectively
when compared to m-CAP. In addition, an enhanced SI-CAP (eSI-CAP) is developed to
address the complexity that arises in SI-CAP at higher modulation order. The results of the
experimental demonstrations in VLC and 10 m SI-POF link shows that when compared with
m-CAP, eSI-CAP consistently yields a data rate improvement of between 7% and 13% for
varying values of the SNR
Study of MIMO techniques for optical wireless communications
No full textWith its huge spectral resource, optical wireless communication (OWC) has emerged as a
promising complementary technology to the radio frequency (RF) communication systems.
OWC provides data communications for a variety of user applications and it can be deployed
using simple, low-cost, low-power and energy-efficient component. In order to enhance
capacity, reliability and/or coverage of OWC, multiple-input-multiple-output (MIMO) systems
are employed to exploit additional degrees of freedom, such as the location and angular
orientation of optical sources and detectors. However, the implementation of MIMO systems is
faced with challenges such as the strong correlation and multipath propagation in indoor OWC
channels, system synchronisation, as well as inter-channel interference (ICI) due to multiple
parallel data transmission. This dissertation investigates MIMO OWC systems which utilises
transmission techniques with reduced complexity. A detailed study and performance evaluation
of the techniques in terms of capacity, spectral efficiency and error rates is conducted through
theoretical analysis, simulation and experiments. The system performance is investigated
under different constraints imposed by impairments such as interference, synchronization and
channel correlation.
Optical spatial modulation (OSM) is studied as a low complexity technique using multiple
light sources to enhance system capacity. A generalised framework for implementing OSM
with energy efficient pulse position modulation scheme is devised. This framework supports
other variants of OSM, and it can be adapted to satisfy varying system requirement such
as spectral and energy efficiencies. The performance of the OWC system is investigated in
indoor line-of-sight (LOS) propagation. The error performance of the system is analysed
theoretically and matched by simulation results. Also, the system performance is evaluated
with experiments to demonstrate feasibility. Furthermore, the performance of OSM MIMO
techniques in the realistic indoor scenario is considered by taking into account the multiple
reflections of the transmitted signal from room surfaces. This is motivated by the recent drive
towards high-speed Gigabits per second (Gbps) data communication, where the inter-symbol
interference (ISI) caused by the multipath propagation may pose a major bottleneck. A model
of the multipath-induced ISI is presented to account for signal spreading and then applied to
formulate the error performance analysis. The impact of multipath-induced power penalty and
delay spread on system performance is demonstrated using their spatial distributions across the
coverage area. Additionally, the impact of timing synchronization problems on the error performance of
different variants of the OSM MIMO techniques is investigated. While most works related
to SM have assumed a perfect synchronization among the multiple transmitter and receiver
elements, such assumption pose a challenge in practical deployment. Hence, the need to
examine the impact of synchronisation error that can result from clock jitters and variations
in propagation delay. Synchronisation error analyses of OSM schemes are presented, and
the tolerance of each scheme to timing synchronization errors is demonstrated. To further
enhance system capacity, this thesis also explores spatial multiplexing MIMO technique with
orthogonal frequency division multiplexing (OFDM). The central objective is to propose and
apply techniques to address the correlation of the indoor optical wireless channel and the
frequency selectivity due to the limited bandwidth of LEDs. To address these two effects,
a joint coding of paired information symbols was applied in a technique termed pairwise
coding (PWC). This technique is based on rotated symbol constellation and it offers significant
performance improvement. The error performance of the proposed system is evaluated through
simulation and experimental demonstration. PWC proved to be effective over varying degrees
of bandwidth limitation and under different channel conditions
Non-linear equalisation techniques for high-speed step-index plastic optical fibre communication
No full textStep-index plastic optical fibres (SI-POF) have become a promising candidate as the media for
short-range in-home and automotive networks due to their low cost and their ease of installation.
However, they have the smallest bandwidth compared to the other optical fibres. Therefore,
high-speed communication over SI-POF results in inter-symbol interference (ISI) that linearly
distorts the signal. Moreover, there are non-linearities from the optical front-end that further
degrade the SI-POF performance.
A straightforward solution is to use non-linear equalisers (NLE) with the SI-POF system as
they compensate for the non-linear distortions while mitigating the channel ISI. Three NLEs
– transversal decision feedback equaliser (DFE), Volterra equaliser/DFE, and the multi-layer
perceptron-based equaliser/DFE (MLPDFE) – have been introduced in the literature. High-order modulation formats – like pulse amplitude modulation (PAM), carrier-less amplitude and
phase modulation (CAP), and discrete multi-tone (DMT) – can be used in combination with the
NLE to overcome the bandwidth limitation further. Thus, the thesis deals with the performance
of these NLEs for PAM, CAP, and DMT transmission in order to achieve high data rates (from
several hundreds of megabits-per-second (Mbps) to gigabits-per-second (Gbps)) in SI-POF.
The contributions of this research work are in threefold: firstly, a simulation model is used to
evaluate and compare the performance of the NLEs for PAM and CAP schemes. The study
shows that for a highly non-linear SI-POF with higher PAM (or CAP) modulation order, the
MLPDFE offers higher data rates than the Volterra DFE followed by the transversal DFE. This
simulation study is further verified with various experiments. For instance, the MLPDFE offers
an error-free bit rate of about 6.2 Gbps over a 30 m SI-POF while the transversal DFE offers
about 5 Gbps at similar SI-POF length. A computational complexity comparison of each NLE
shows that the transversal DFE requires the least computing requirement, and the VOLT2DFE
has higher computational order than the MLPDFE.
Secondly, the work investigates a recently introduced frequency domain NLE (FD-NLE) for
DMT transmission over SI-POF. It explores the performance of the FD-NLE for DMT with
clipping distortion in a highly non-linear SI-POF system. The FD-NLE is shown in this case as
the better choice than the conventional frequency domain equaliser. With insight from the FD-NLE for DMT, both Volterra and the MLP equalisers are translated to the frequency domain for
PAM and CAP transmission over SI-POF. A computational complexity analysis shows that implementing the NLEs (with PAM and CAP) in the frequency domain reduces their complexity
by at least 60% if there are more than 16 feedforward taps for the equaliser.
Finally, extensive experiments are carried out to evaluate and compare the bit error rate (BER)
performances and the computational complexity of the modulation schemes with their respective NLEs. The comparisons show that for a short-length SI-POF of up to 30 m, representing
benign channel conditions, bit-loaded DMT with FD-NLE offers the best performance requiring the least complexity and the least transmitted electrical power. However, at longer lengths,
PAM with MLPDFE gives the best performance. CAP with the MLPDFE demands the highest
computational complexity and the transmitted electrical power
Dostępność oraz korzystanie z usług przez wiejskie społeczności przygraniczne w południowo-zachodniej Nigerii
No full textBorderland communities hold a strategic position in many countries. However, in spite of this, many of these communities, specifically in Nigeria, are still characterized by neglect and underdevelopment. Based on the above fact, this study explores the service deprivation and coping strategies of rural borderland communities in South-Western Nigeria. The study revealed that the majority of inhabitants of rural borderland (64.0%) get their water supply straight from streams and are bound to cover distances of 500 meters or longer to collect water. Similarly, the majority of them defecate in bush reserves around their houses. Also, the study showed that people can travel across the national border to neighboring countries on a regular basis to access basic services, like healthcare facilities. Likewise, medical personnel or attendants from neighboring countries or towns are called during critical or serious illness to render services which the Nigerian Government does not provide. The development of Nigeria’s frontier areas is therefore of paramount importance and really pending, and must be made priority in urgent and major developmental actions taken in the country.Społeczności przygraniczne odgrywają strategiczną rolę w wielu krajach. Jednakże, pomimo tego faktu, wciąż aktualną, charakterystyczną cechą wielu z takich społeczności, szczególnie w Nigerii, jest zaniedbanie i niedorozwój. W oparciu o powyższy fakt zbadano poziom niedoboru usług i strategie radzenia sobie z nim przez społeczności przygraniczne w południowo-zachodniej Nigerii. Badanie wykazało, że większość mieszkańców obszarów wiejskich pogranicza (64,0%) zaopatruje się w wodę prosto ze strumieni i jest zmuszona do pokonania odległości 500 metrów lub więcej w celu zebrania wody. Podobnie większość z nich nie korzysta z toalet, lecz krzewów wokół swoich domów. Badanie pokazało również, że ludzie mogą regularnie przekraczać granice sąsiednich krajów, aby uzyskać dostęp do podstawowych usług, takich jak placówki opieki zdrowotnej. Jednocześnie, personel medyczny lub stażyści z sąsiednich krajów lub miast są wzywani w sytuacjach krytycznych lub poważnej chorobie, aby świadczyć usługi, których nie zapewnia rząd Nigerii. Rozwój obszarów przygranicznych Nigerii ma zatem ogromne znaczenie i musi stać się priorytetem w działaniach rozwojowych podjętych w tym kraju
BPSK subcarrier intensity modulated free-space optical communications in atmospheric turbulence
No full textFree-space optical communications (FSO) propagated over a clear atmosphere suffers from irradiance fluctuation caused by small but random atmospheric temperature fluctuations. This results in decreased signal-to-noise ratio (SNR) and consequently impaired performance. In this paper, the error performance of the FSO using a subcarrier intensity modulation (SIM) based on a binary phase shift keying (BPSK) scheme in a clear but turbulent atmosphere is presented. To evaluate the system error performance in turbulence regimes from weak to strong, the probability density function (pdf) of the received irradiance after traversing the atmosphere is modelled using the gamma-gamma distribution while the negative exponential distribution is used to model turbulence in the saturation region and beyond. The effect of turbulence induced irradiance fluctuation is mitigated using spatial diversity at the receiver. With reference to the single photodetector case, up to 12 dB gain in the electrical SNR is predicted with two direct detection PIN photodetectors in strong atmospheric turbulence
Resilient LiFi for internet-of-things
No full textNumerous research studies have been conducted to investigate alternative wireless communication technologies in response to the growing data traffic demands. At this point, light fidelity (LiFi) has emerged as a promising solution to meet future data requirements. In LiFi systems, data is transmitted by rapidly turning a light-emitting diode on and off, a process imperceptible to the human eye. This technology offers several advantages, including a wide unlicensed spectrum, enhanced security, affordability, and high data rates. However, further investigation is necessary to overcome existing challenges and fully exploit the potential of LiFi networks.
This thesis aims to enhance mobility management and cooperation techniques in LiFi systems, with a specific focus on addressing the limited coverage inherent to optical spectrum. To overcome this coverage limitation, the multi-tier LiFi networks and the integration of two cooperation techniques, namely device-to-device (D2D) communication and coordinated multi-point joint transmission (CoMP-JT), are investigated. Moreover, the precise indoor positioning, high reliability, and low latency capabilities of LiFi make it highly suitable for industrial internet-of-things (IIoT) networks. As a result, this thesis explores various industrial applications, including time synchronization (TS) and unmanned aerial vehicle (UAV) swarm networks, to harness the advantages offered by LiFi technology
MIMO free-space optical communication employing subcarrier intensity modulation in atmospheric turbulence channels
No full textIn this paper, we analyse the error performance of transmitter/receiver array free-space optical (FSO) communication system employing binary phase shift keying (BPSK) subcarrier intensity modulation (SIM) in clear but turbulent atmospheric channel. Subcarrier modulation is employed to eliminate the need for adaptive threshold detector. Direct detection is employed at the receiver and each subcarrier is subsequently demodulated coherently. The effect of irradiance fading is mitigated with an array of lasers and photodetectors. The received signals are linearly combined using the optimal maximum ratio combining (MRC), the equal gain combining (EGC) and the selection combining (SelC). The bit error rate (BER) equations are derived considering additive white Gaussian noise and log normal intensity fluctuations. This work is part of the EU COST actions and EU projects
Coherent polarization shift keying modulated free space optical links over a Gamma-Gamma turbulence channel
No full textProblem statement: The optical signal propagating through the Free Space Optical (FSO) channel suffers from irradiance and phase fluctuations caused by the atmospheric turbulence, which results in Bit Error Rate (BER) performance degradation.
Approach: In this study the performance of the Multilevel Coherent Polarization Shift Keying (M-POLSK) based FSO communication system operating over the gamma-gamma turbulence channel is investigated. To mitigate the turbulence induced fading, the convolutional coding and spatial diversity techniques are employed. The upper BER bounds are derived using the transfer function technique.
Results: For example, with a SNR of 30 dB, the BERs for uncoded and coded M-POLSK are 0.047 and 1.4×10-4, respectively in the weak turbulence regime. When the Maximum Ration Combining (MRC) technique employing four detectors are used in the receiver, the power gains of ∼31.4, ∼29.5 and ∼57.9 dB are achieved for weak, moderate and strong turbulence regimes, respectively.
Conclusion: We have also shown that the spatial diversity offers increased link margin as the scintillation level rises. Compared to the angular modulation, the proposed M-POLSK scheme offers high immunity to the phase noise, thus reducing the power penalties
- …
